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Troubleshooting headlights

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  • Electrical: Troubleshooting headlights

    1950 Champion.
    Left headlight only works on high beam. Right headlight works on both low and high beams. Parking lights are OK.

    First thought was that it was a bad bulb. Replaced bulb but same symptoms.Tried a known working bulb without success.

    Would the dimmer switch affect only one headlight? More likely in the wiring? Do these things have a lighting relay?

    Looking for ideas of likely trouble areas. All suggestions welcome.


  • #2
    The bulb uses the same ground for Hi and Lo. The (tri) socket is likely the issue. The supply (-6) contact for the low beam may be corroded/broken. Pull the bulb and use a VOM to check for voltage on each contact. The ground should have continuity, while the supply should be (-6) to each filament ( using the hi/lo dimmer switch)
    64 GT Hawk (K7)
    1970 Avanti (R3)


    • #3
      There are no relays, but there are terminal blocks on the right and left sides of the engine compartment. There is one terminal apiece for hi-lo-park. A few moments with a test lamp will show if you have lo beam power there, and then you can trace out to the bulb socket. Good chance the problem is the socket.


      • #4
        Remove the headlight and power up the contacts to confirm the unit. If it is ok then start tracing back for an open.


        • #5
          There should be a Circuit Breaker, usually on the Hd. Lt. Switch, but it controls Left AND Right side, AND High and Low Beam, so since you do have some power it is not the problem.

          As mentioned, the Terminal Block near the Radiator is a good place to check for Power.
          Second Generation Stude Driver,
          Proud '54 Starliner Owner


          • #6
            Problem solved

            Thanks to all who commented. I started looking at the tri-connector and terminal block. Things were just not adding up, especially when comparing to the opposite side. I continued following the bundle of wires coming from the terminal block and heading toward the firewall. It was there that I found one of the metal cable clips that was heavily crimped across the wire bundle. I removed the wires from under the clip and found that the insulation was compromised. Once I fixed this problem, the lights worked fine. Yay!


            • #7
              THANK you, for the follow up...